Bungy jumping, one of the world's biggest tourism phenomena, is 25 years old today and the two co-founders of the heart-pumping activity are reuniting for an anniversary party in Queenstown, where it took off.

AJ Hackett, a carpenter, ski bum and encyclopaedia salesman, and Henry van Asch, a farmhand and a speed skier who clocked almost 200 km/h, set up shop for their daring enterprise in an old bus at the Kawarau Bridge on November 12, 1988.

"The reception desk was an old card table," Hackett recalled this week.

"We never doubted that bungy jumping would last but we didn't know if we could manage it ourselves and whether other operators would come along and stuff it up. But from the very first jumps, we knew it was something very special."

Since the modest start, it's estimated that at least 4.5 million people around the world have taken a bungy jump, 75 per cent of them with the AJ Hackett brand, which has had no fatalities.

Things can go awry, however. In one dramatic incident last year, an Australian tourist jumped with another company in Zambia and ended up plunging into the rapids in the Zambezi River after her bungy cord broke.

She survived, but others haven't. Among the fatalities, an Italian couple died during a tandem bridge jump in Italy.

The first "commercial" jumper coaxed off the Kawarau Bridge by Hackett and van Asch was one of their "ski bum" mates, Jef Desbecker, now a veteran Kiwi heli-skiing guide.

Ever since Desbecker took the 43-metre dive, there has been a steady flow of people following him over the edge, making Hackett and van Asch millionaires many times over.

Van Asch said: "It's a bizarre physical activity that brings elation and, afterwards, contemplation. It is a very individual thing and engages your psyche. It doesn't happen in a matter of seconds. It takes some people minutes, hours, days, months or years to jump. When they come out of it they say 'holy shit', I can do anything."

About 100,000 people a year take the leap of faith in NZ, which is still the spiritual home of bungy, although it has a foothold in several countries.

The co-founders split as business partners in 1997 (some say it was amicable, others bitter) with van Asch taking over the New Zealand operation and Hackett the rest of the world.

Some of Hackett's global bungy sites include Australia, France, Germany, Bali and Macau (the highest bungy at 233 metres).

The next to open will be in the 2014 Winter Olympics city of Sochi, Russia, and then Sentosa Island in Singapore.

The idea for bungy came to Hackett from Vanuatu, where villagers jump from towers with vines tied around their ankles.

Hackett substituted the vines for a bungy (a word that comes from Kiwi slang and roughly means "elastic strap") and recruited van Asch to help him get the business off the ground.

"A big challenge early on was from the 'cowboy operators'," Hackett said. "Bungy would go through boom and bust cycles, dictated by accidents. But the cowboys are pretty much gone now. It has matured."

Hackett, who has lived in France and now Singapore, has flown in from Sochi to be with van Asch for Tuesday's 25th anniversary bash for up to 400 people.

Their previous parties at the Kawarau Bridge have resulted in nude bungy jumping and this one promises "something to do with motorbikes and a bus", a company spokesman let slip.

But it doesn't take a party to convince people to jump in the nude.

Comedian Billy Connolly once did it and many others have left their pants behind.

Celebrity jumpers (clothed) have included golf champion Tiger Woods, Lord of the Rings star Orlando Bloom, singer Katy Perry, soccer whiz David Beckham and even a sheikh from Abu Dhabi.

However, AJ Hackett Queenstown sales manager Regan Pearce says the most dominant group of jumpers is backpackers.

After all these years, the co-founders still have their nerve and continue to jump. Van Asch has jumped about 600 times and Hackett more than 1000, including an illegal publicity stunt off the Eiffel Tower in 1987, and many out of helicopters.

"After 25 years, we have just gone through round one really," Hackett said. "There is a whole new generation [of potential jumpers] coming through now."